Tunnel kiln for firing ceramic articles



March 6, 1956 G. M. J. CREMER TUNNEL KILN FOR FIRING CERAMIC ARTICLESOriginal Filed Sept. 24, 1949 7 Sheets-Sheet 1 mmvmk March 6, 19 G. M.J'. CREMER TUNNEL KILN FOR FIRING CERAMIC ARTICLES Original Filed Sept.24, 1949 7 Sheets-Sheet. 2

INVENTOP March 6, 1956 ca. M. J. CREMER TUNNEL KILN FOR FIRING CERAMICARTICLES 7 Sheets-Sheet 3 Original Filed Sept. 24, 1949 WED March 6,1956 G. M. J. CREMER 2,735,943

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TUNNEL KILN FOR FIRING CERAMIC ARTICLES 7 Sheets-Sheet 5 km PFI PP I KMarch 6, 1956 Original Filed Sept. 24, 1 949 March 6, 1956 G. M. J.CREMER 2,736,943

TUNNEL KILN FOR FIRING CERAMIC ARTICLES Original Filed Sept. 24, 1949 7Sheets-Sheet 6 Q 1 I A }W.LMLW

March 6, 1956 G. M. J. CREMER 2,736,943

TUNNEL KILN FOR FIRING CERAMIC ARTICLES Original Filed Sept. 24, 1949 7Sheets-Sheet '7 2,736,943 Fatented Mar. 6, 1956 2,736,943 TUNNEL KILNFOR FIRING CERAMIC ARTICLES Gottfried Maria Josef Crerner, Frechen, nearKoln, Germany Original application September 24, 1949, Serial No.

117,693, now Patent No. 2,625,730, dated January 29,

1953. Divided and this application January 14, 1953,

Serial No. 331,175

9 Claims. (Cl. 25142) This invention relates to a tunnel kiln for firingceramic products which is not only suitable for firing the fine ceramicand refractory products hitherto customarily treated in tunnel kilns,but also mass-produced goods, such as tiles, roof tiles, and stoneware.

The invention refers particularly to the providing of means which allowa practically continuous transport of the usual carriages on which thegoods to be burned are mounted through the kiln and to means enablingthe regulation of the cooling operation in the kiln.

An object of the invention is to produce a new and improved kiln havingthe features of construction, arrangement and operation hereinafterdescribed.

According to the invention the interior of the kiln is closed in respectof the outer atmosphere constantly during the advance of the firingcarriages through the kiln passage by slide plates removably carried bythe firing carriages only through a small section in the region of theadmission end and only a small section in the region of the outlet endof the kiln. Suitable sealing is provided between the slide plates,carriages and kiln walls to prevent axial air flow. Said slide platesare introduced into and removed from the kiln through slots arranged inthe walls of the kiln.

According to a further feature of the invention means are provided foroperating the cooling zone of the tunnel kiln in such manner that in thefirst section of the cooling zone indirect, abrupt cooling takes placeby means which suddenly remove heat, and in a following section of thekiln, in which transcrystallization takes place, there is a slow furthercooling by additional cooling means, which in turn is followed by themost rapid possible withdrawal of heat through indirectly acting coolingmeans, this being followed in turn by final direct cooling by fresh airsucked out of the outlet end of the kiln. Such operating means consistsof a number of heat exchangers, which are preferably metallic, throughwhich cooling agents flow, and which are disposed in the arch and/or inthe side walls of the kiln passage, their distribution preferably beinguniform. By switching on and off a larger or smaller number of said heatexchangers and/or regulating the amount and speed of the cooling agentsflowing through them, and by regulable screening of the heat exchangersthe cooling zone is controlled. For this purpose use is made oftemperature resistant slides, which are preferably made of ceramicmaterial, and cover the heat exchangers to a larger or smaller extentindividually or in groups, and are operated from outside the kilnpassage.

This renders possible a fine regulation of the coolingdown curve andhence the adjustment of a cooling-down curve which is optimum for theparticular ware to be fired, or of the corresponding temperature, forexample not only in the middle of the cross-section of the kiln passage,but at every point of the latter. Because of the complete utilization ofthe cooling possibilities in the entire cooling range of the kilnpassage, a substantial shortening of the total length of the coolingzone is possible in comparison with that otherwise required.

The heat exchangers, in accordance with a further feature of theinvention can be provided not only in the cooling zone, but alsoadditionally atthe end of the firing zone and in the direct proximity ofthe burners. The heat exchangers permit in addition the production ofthe amount of heat required in each particular case for the totaloperation for the manufacturing plant in question, by switching on oroff more or less of these units. In this way heat can be regained fromthe individual groups of-cooling units-also in accordance with thetemperatures which prevail in the kiln passage at the respectivepointsfrom the cooling media heated to different temperatures, inaccordance with the purpose for which it is to be used, in the form ofhot water, saturated steam, high pressure hot water, or superheatedsteam. The portion of the cooling zone which follows the indirectlycooled zone is cooled directly, namely by means of fresh air sucked inthrough the gateless, i. e. open outlet end of the kiln, which is closedoff from the indirectly heated part and hence from the interior of thekiln. Since the temperature of this cooling air is not too high, it mayundergo intermediate heating, for example by passage through one or moregroups of the different heat exchangers, in which the appropriateconditions of temperature exist, and thereby be brought to the mostconvenient temperature for the relative part of the preheating zone. Thesmoke section is in this connection so constructed, that through theprovision of openings, which are not situated opposite one another, inthe walls of the kiln passage, the hot air flowing through this zone anddrawn off out of the outlet end is guided to and fro, so that the wareis swept over by the hot air on all sides in the most favourable manner.

A part of the hot air produced by means of the heat exchangers from thefirst, indirectly cooled section may of course also be used in knownmanner as preheated air for combustion and supplied to the burners orfurnace. Air for combustion preheated to far higher than 350 6., whichhitherto was regarded as the maximum attainable temperature, can beobtained in this manner.

As a supplement to the step described, in accordance with a furtherfeature of the invention, the actual combustion zone of the kiln passagecan be constructed'with double walls, so that additional amounts of heatcan be gained from the space between, while avoiding radiation losses,which are the greatest precisely from the firing zone section.

The obtaining of additional amounts of heat which are needed onlyoccasionally by heat exchangers which are disposed in the actual firingzone or in the vicinity of the burners does, it is true, entail anincrease in the fuel consumption, but in view of the possibility ofproducing this additional amount of heat, which usually is required onlytemporarily, in the simplest possible manner, this is not a seriousconsideration. On the other hand, the operation of separate steam plantsfor these purposes, which is usually necessary precisely in the coarseceramic industry, such as the tile and roof tile industry, can as aresult be dispensed with.

Since the heat exchangers, as described, can be screened, the kiln canbeoperated in such manner that per se a water and steam capacity can beobtained which is suflicient for the winter months, while during thesummer months sections of the heat exchangers are screened or otherwisecut out, and thus the entire kiln is operated with reduced production ofhot water or steam. with a correspondingly lower fuel consumption.

Finally the thermal efficiency of the tunnel kiln is im proved byreducing the radiation losses to a minimum, because the heat exchangersreceive the heat, which would otherwise be lost by radiation through thewalls.

The invention is described below in detail with reference to thedrawings, which illustrate a tunnel kiln constructed in accordance withthe invention, without the invention, however, being restricted withregard to its structural performance to the exemplified embodimentillustrated in the drawings. On the contrary, numerous modifications arepossible without departing from the basic principle of the invention.

The drawings illustrate a tunnel kiln according to the invention, and inthe same:

Figures 1 and la show a diagrammatical view of the whole kiln.

Figure 2 shows in an enlarged scale a longitudinal section through thesharp cooling zone.

Figure 3 shows a plan view corresponding to Figure 2.

Figure 4 shows a longitudinal section through the end of the coolingzone,

Figure 5 shows a plan view corresponding to Figure 4,

Figure 6 shows a section on the line VIVI in Figure 2, and

Figure 7 shows a section on the line VIIVII in Figure 2.

The tunnel kiln consists, as is to be seen from Figures 1 and la, of thepreheating zone, the firing zone and the cooling zone, through which thecarriages are practically continuously advanced by means of theadvancing or propelling device 33.

Figures 1 and 5 show the vertical slots 23 and 24 provided in one of theside walls of the kiln through which the slide plates 21, which effectthe closing-off of the kiln passage against the outer atmosphere andwhich are carried by the firing carriages 28 over short sections, areintroduced and removed. These slide plates, suspended from grippertrolleys 22, are returned by means of return rails 22 after theirremoval from the kiln passage.

The slot 23 is between the preheating zone and the firing zone, andserves for the removal of the slide plate 21 mounted on the carriagebefore entering the kiln.

The slot 23 is arranged substantially beyond the slot 20 approximatelymidway of the cooling zone of Figure 1. A slot 24 in advance of the slot23 is disposed a distance of the length of at least one carriage,preferably two or three up to four carriages from the end of the kiln.The slot 23 serves for introducing a slide plate and the slot 24 fortaking out this slide plate.

The best spacing of the slots of each pair is selected according to theparticular working conditions.

The slide plates 21 consist of metal plates corresponding to the form ofthe firing conduit cross-section. These plates are provided at the edgeswith flexible packings 25 which bear against the wall and the arch ofthe firing conduit and thus effect a shutting off with respect to thewalls of the firing conduit. The packing can consist of metal brushes.It has been found particularly suitable to use steel brushes. Thebrushes form a kind of labyrinth seal which at the given pressures andgas velocities provides a sufficient sealing preventing the axial flowof air through the firing conduit. Instead of wire brushes packingsconsisting of glass wool, asbestos, or the like, can be used, thesesubstances being reinforced by Wire, fabric or the like.

The slides are so formed that they can be arranged at one end of everycarriage and supported on the carriage platform by feet 29. The slots20, 23 and 24 in the conduit walls are enlarged at the bottom as at 31,so that the feet 29 can pass therethrough.

To seal the platforms of the carriages 28 with respect to the side wallsof the tunnel, brush packing joints 3 are provided on the side walls ofthe kiln channel over an extent amounting to at least the length of onecarriage in front of the withdrawal slot of the cooling zone and withinthe range of the entry end of the oven. These brushes are preferably ofreversed U-shape (Figure 4) and the edges of the ceramic carriageplatforms are, contrary to previous practice, not profiled but madesmooth.

Additionally sealing between the adjacent edges of the carriages hasalso to be provided in a suitable way, for example by interengagingparts of said edges.

1 By the described arrangement of the slide plates cooperating withsealing means a satisfactory seal is obtained of the interior of thekiln consisting of the preheating, firing and indirect cooling zones.Such seal is effective during the movement of the carriages, so thatpractically continuous progress of the firing carriages through the kilnis made possible.

As the introduction and withdrawal of the slide-plates during working isvery simple and can be carried out extraordinarily rapidly, inparticular when using suitable gripping devices, only short stoppingperiods to perform this operation are necessary. These pauses do notinterrupt the practically continuous working process. The hydraulicallydriven advance device 33 is so adjusted that on termination of oneforward stroke given by the length of the piston of said device oneslide-plate will have reached the withdrawal slot, so that the lattercan be withdrawn during the inactive return stroke of the piston.

The construction of the cooling zone according to the invention isparticularly shown in Figures 27. in Figure 2 is indicated a dotted line19 showing the characteristic shape of the cooling curve obtainedaccording to the invention.

In the part of the cooling zone which directly follows the firing zone,and in which cooling takes place for example from 1460" to 660 or 700,there are provided in the kiln walls metallic heat exchangers 5, 6, '7,i0 and 11 (Figures 1, 2 and 6), which are advantageously provided bothin the side walls and in the arch. Contrarily to the exemplifiedembodiment, they may also run vertically or obliquely in the walls.

On account of the very high temperatures prevailing here, the heatexchangers in the first part of the cooling zone are preferably cooledby air. In the exemplified embodiment they are in fact in heat exchangerelation to pipes 12 which supply the already preheated air out of thecooling end, which air is then, after flowing about the heat exchangers,passed on to the preheating zone through pipes 13 and introduced intothe latter. Rising pipes leading to the burners 16 supply the latterwith preheated air for combustion. The heat exchangers may also be0perated with cold fresh air. The above mentioned and illustratedembodiment is however particularly advantageous in respect of the bestpossible thermal efiiciency.

In addition to these heat exchangers, further bank 1 and 3 of such heatexchangers (Figures 1 and 2) which are traversed by water can bedisposed in the kiln arch, and as shown, these banks are connected withthe banks 5, 6 and 7 by common inlet and outlet pipes 4 and 4'respectively.

In the above described sharp cooling section C (Figure 1) of the coolingzone, the purpose of which is to lower the temperature of the fired wareto the critical point in the minimum time, the kiln passagecross-section is advantageously equal to that in the firing zone.According to the preferred embodiment of the invention, as illustratedin Figure 2, it is thereupon increased, in order thus to provide a freespace above the firing carriages, in which the hot air produced (whichis in any case ineffective for heating purposes) will collect.

In the first part of this latter zone C increased in height, whichconstitutes one of the important danger zones, preferably no specialcooling means are installed, so that the cooling operation may takeplace as slowly as possible here. Sharper cooling starts only a fewsections further on, namely after the temperature has fallen to 500 andlower. In the cooling zone there are provided in the arch of the kilnpassage 2, covering the former entirely or partially, and preferablyalso in the side walls, banks of heat exchangers 1, 3 in the form ofsteel tubes, which are connected to a tube system 4, and through whichthe cooling water enters at a suitable point. These heat exchangers,which can be connected and disconnected in groups, are preferably socontrolled that one of them may act as preheater, while the next one maybring the temperature of the water to the temperature of use.

The banks of heat exchangers are illustrated only diagrammatically inFigures 2, 3, 6 and 7, and alterations are possible as to theirarrangement, without departing from the principle of the invention.

The amount of heat given up to the heat exchangers is controlledaccording to the invention by temperature-resisting, preferably ceramicslides, which are so disposed that they screen the heat exchangers to alesser or greater extent in respect to the firing passage, as shown inparticular in Figure 6. The slides 17 are located beneath the heatexchangers 6, when they are closed, separate 011 the arch space. Theyare operated by rods 18. Manufacture of the slides from ceramic materialensures that, when the slides are closed, the screened-01f section ofthe respective heat exchangers absorbs practically no heat. These slidesmay of course not only serve to control in a desirable manner thetemperature in the firing passage itself, but at the same time also tocontrol the temperature of the cooling medium or of the air to bepreheated.

With the aid of the radiation of heat to the heat exchangers which isregulable by means of the slides 17, it is possible to ensure over theentire cross-section of the passage the desired temperature curve in thesharp cooling zone and the final cooling zone. The temperature curve mayfor example have the shape shown in the broken line 19 in Figures 2 and4. It is there shown that the temperature drops more or less abruptlyfrom about 1400" upwards to a temperature of about 600, then constantlydeclining to about 40 over the further longitudinal extent of thefurnace. Any other shape of the cooling curve can be adjusted in similarfashion, if the ware fired demands this.

With regard to the actual firing zone, apart from the previouslymentioned arrangement of the heat exchangers for producing additionalheat in the direct proximity of the burners, the additional devices inaccordance with the invention are restricted to the double-walledconstruction of the firing zone, which can be seen from thecorresponding drawings (Figure 6, outer casing 48).

The form of construction of a tunnel kiln, described in detail hereinabove and illustrated in the drawings, for carrying out the invention,is naturally only an example and can be varied in various ways withoutdeparting from the basic principles of the invention, while theinvention is furthermore not restricted to the simultaneous use of allthe measures described, but certain of them individually will alsoalready lead to considerable improvements as compared with the method ofworking hitherto known.

This application constitutes a division of my application Serial No.117,693, filed September 24, 1949, and entitled Process for FiringCeramic Articles, now Patent 2,625,730, dated January 20, 1953.

I claim:

1. An open-ended tunnel kiln having successively arranged preheating,firing and cooling zones, said kiln comprising carriage means forprogressing articles to be fired through the kiln, metallic heatexchangers within the cooling zone, and sealing means detachably mountedon the carriage means and movable therewith thereby to seal the heatexchangers from the other kiln portions.

2. An open-ended tunnel kiln as claimed in claim 1, in which the sealingmeans comprise high temperature resistant slides of ceramic material ofa shape similar to the cross sectional dimension of the kiln interior.

3. An open-ended tunnel kiln having successively arranged preheating,firing, and cooling zones, said kiln comprising carriage means forprogressing articles to be fired through the kiln, metallic heatexchangers within the cooling zone, means for recurrently screening theheat exchangers from adjacent portions of the interior of the kiln,slide plates, the tunnel having slots respectively in the cooling zoneand near the entrance to the kiln through which said slide plates may beintroduced into and removed from the kiln means on the carriage meansfor mounting said slide plates on the carriage means, and means on theoutside of the kiln for introducing and removing the slide platesthrough the slots respectively to and from the carriage means.

4. An open-ended tunnel kiln as claimed in claim 1, in which certain ofsaid metallic heat exchangers are arranged in the cooling zone adjacentthe firing zone, the next successive portion of the cooling zone beingfree of heat exchangers, metallic heat exchangers in the final portionof the cooling zone, the last-named heat exchangers being spacedsubstantially from the outlet end of the kiln, the outside air effectingdirect cooling of the outlet end of the kiln, and means for supplyingcooling media to said metallic heat exchangers.

5. Apparatus of the class described, comprising a tunnel kiln havingpreheating, firing and cooling zones, firing carriages movable throughthe tunnel kiln, slide plates removably carried by said carriages, meansto effect a seal between said carriages and the kiln walls, said kilnhaving spaced slots enabling the slide plates to be mounted upon thecarriage through one slot and removed from the carriage through theother slot from the outside of the kiln, and means on the outside of thekiln for conveying the slides from one slot to the other.

6. Apparatus of the class dsecribed, comprising a tunnel kiln havingpreheating, firing and cooling zones, firing carriages movable throughthe tunnel kiln, slide plates removably carried by said carriages, meansto effect a seal between said slide plates on the carriages and the kilnwalls, said kiln having spaced slots enabling the slide plates to bemounted upon the carriage through one slot and removed from the carriagethrough the other slot from the outside of the kiln, and means on theoutside of the kiln for conveying the slide plates from one slot to theother, said conveying means including a slide plate gripping device andby-pass rails.

7. Apparatus of the class described, comprising a tunnel kiln havingpreheating, firing and cooling zones, the cooling zone including a sharpcooling section, firing carriages movable through the tunnel kiln, slideplates removably carried by said carriages, means to eifect a sealbetween said slide plates on the carriages and the kiln walls, said kilnhaving spaced slots enabling the slide plates to be mounted upon thecarriage through one slot and removed from the carriage through theother slot from the outside of the kiln, and means on the outside of thekiln for conveying the slide plates from one slot to the other, saidconveying means including a slide plate gripping device and by-passrails, one slot being between the preheating zone and the firing zoneserving for the removal of a slide plate, a further slot being at theend of the sharp cooling section serving for the introducing of a slideplate, and a further slide removal slot disposed at a distance from theoutlet end of the kiln at least equal to the length of one carriage.

8. Apparatus of the class described, comprising a tunnel kiln havingpreheating, firing and cooling zones, carriages movable through thetunnel kiln, slide plates removably carried by the carriages, said kilnhaving spaced slots enabling said slide plates to be mounted upon thecarriages through one slot and removed from the carriage through anotherslot in a subsequent area from the outside of the kiln, said slideplates having forms corresponding substantially to the cross section ofthe inside of the kiln, and flexible packing on the edges of the slideplates for slidably sealing the slide plates against the kiln walls.

9. The combination claimed in claim 8, and brush seal ing means affixedon the interior of the kiln respectively in the preheating and coolingzones, said brush sealing means having dimensions lengthwise of thetunnel approximately equal to the length of said carriages and engagingagainst said carriages.

References Cited in the file of this patent UNITED STATES PATENTS248,801 Sebillot Oct. 25, 1881 1,361,977 Fuller Dec. 14, 1920 1,503,750Dressler Aug. 5, 1924 1,610,968 Robertson Dec. 14, 1926 1,913,302 BarkerJune 6, 1933

